At least 10 times in the last two months, crackling gunfire just outside the Uere special needs school has sent students and teachers diving to the floor as heavily armed gangsters warred among themselves and sometimes with police in the Rio slum of Mare.

With rival drug dealers on practically every corner and a militarized campaign by authorities to take them out, shootouts have become so common that the school holds drills for students to practice taking cover quickly.

"After [a shootout] it's not possible to teach," said Yvonne Bezerra de Mello, the founder of Uere, which offers classes for underprivileged students with learning difficulties. "So we just play and talk, because some of the children get really nervous."

Brazil's most famous city has long struggled with violence, particularly in the hundreds of slums controlled by drug traffickers. But amid a punishing economic crisis, some studies suggest 2016 was Rio's most violent year in decades despite a police pacification program that was meant to curb slum violence ahead of last year's Olympic Games.

Crime still seems to be rising: In January and February, homicides rose 17 and 24 percent, respectively, compared to the same months last year, according to Rio state government crime statistics.

And schools are increasingly caught in the crossfire.

Every day, shootouts force the closure of between 20 and 30 schools or day care centers, according to Cesar de Queiroz Benjamin, the city's public schools chief, resulting in 6,000 to 7,000 children being sent home. If this rate continues, Rio will far exceed the 1,500 closures it saw last year.

"It has clearly gotten worse," Benjamin said.

This April 12, 2017, photo shows a bullet hole on the front gate of a school in Acari, Rio de Janeiro, Brazil, where 13-year-old Maria Eduarda Conceicao was shot and killed when she was caught in the crossfire of a lengthy shootout between police and gangsters.

Girl shot, killed

The toll the violence takes on children attracted national attention on March 30 when a 13-year-old girl was shot and killed at a school in Acari, a poor northern neighborhood, when she was caught in the crossfire of a lengthy shootout between police and gangsters.

Maria Eduarda Conceicao was hit by several rounds at the school entrance as she walked to the water fountain after physical education class. Large bullet holes can still be seen on the school's outer wall and front gate, a grim reminder for students, teachers and parents arriving every day.

An autopsy confirmed one of the bullets that hit Conceicao was a 7.62 mm round, fired from a military-grade rifle in the hands of police. Cellphone video shot by a bystander and widely circulated in local and social media showed two officers continuing to fire at armed but apparently wounded suspects lying on the ground in front of the school. The two officers have been indicted in the killings.

When the video is magnified, Conceicao's lifeless body can be seen on the school grounds.

"We should all feel very humiliated and ashamed," Rio de Janeiro Mayor Marcelo Crivella said after attending Conceicao's funeral this month. "This cannot happen again."

Roberto Sa, the head of security for Rio de Janeiro state, has opened an investigation into Conceicao's death, and civil police are also investigating. But Sa said there is little military police can do other than shoot back when they confront heavily armed suspects. He said lawmakers should impose harsher penalties for possession of illegal firearms.

A police officer checks the bullet holes in the wall of the school where Maria Eduarda Conceicao was killed by a stray bullet during a shootout between police and alleged drug traffickers in the Acari neighborhood, in Rio de Janeiro, Brazil, April 12, 2017.

Children 'aren't safe anywhere'

Security in Rio de Janeiro is the responsibility of the state, not the city government, limiting what Crivella can do to address the problem. But he has promised to apply special bulletproof coating to walls around at least 10 schools in areas considered conflict zones like Mare.

Benjamin, the education secretary, and Bezerra de Mello, the Uere school's founder, argued that bulletproofing would just paper over the root causes of the violence. And Bezerra de Mello said such a wall won't necessarily keep her students safe, since the rounds sometimes come from above.

Last month a helicopter taking part in a police operation hovered over her school and opened fire for several minutes, with some of the rounds striking the building. Nobody inside was hurt, but afterward she installed a bright yellow sign on the rooftop that reads, in big, black capital letters: "SCHOOL, DON'T SHOOT."

Bezerra de Mello said that beyond the question of whether bullets breach the school's walls, her 300 students still have to deal with rampant crime in their neighborhoods when class lets out. Up to 90 percent of them, she estimated, have learning disorders linked to the violence and trauma they experience on a daily basis.

She recently asked a class of 14 students in their early teens how many had lost a family member to gun violence. Six raised their hands.

"The children aren't safe anywhere," Bezerra de Mello said, "They wake up to the sound of gunshots and go to bed to the sound of gunshots. ... They see death at every corner."